In testing and mounting semiconductor devices it is necessary that the leads of the device be correctly positioned and the ends of leads lie in a common plane. This is particularly true for surface-mount devices. The leads of the semiconductor device may be bent side ways, out, in or down moving the end of the pin from a plane common with the ends of the other pins. In some instances, one or more pins may have a greater height than the others.
Existing planarity inspection equipment is either not cost-effective or performs the inspection "off-line" as in a quality control operation. The hardware required for off-line inspection is inexpensive, however, the inspection is done manually, lead by lead, making 100% inspection time consuming as well as cost prohibitive. Automatic equipment which can be used for on-line inspection is actually stand-alone equipment integrated with the other processing equipment.
In lead inspection systems in which CCD cameras are used, either the device is rotated to present both sides of the device to the same optics and the CCD camera or two separate sets of optics and cameras are used to view both side of the device simultaneously. Either method requires additional image capture and processing time, and usually additional hardware.
The lighting of the leads is critical to capture an accurate image for determining the position of each lead. Therefore, the lighting must be directed toward the leads to provide optimum illumination for the optical system that is imaging the leads.